A fiber-reinforced composite plastic product, which is one of fiber-reinforced composite materials, has been widely used in sports and leisure goods and in industrial products such as vehicles or aircrafts, due to its light weight, high mechanical strength and high rigidity.
Among fiber-reinforced composite plastic product s, a fiber-reinforced tubular composite is, for example, used in sports and leisure goods such as fishing poles, shafts for golf clubs, ski poles, and bicycle frames.
Examples of a method of manufacturing a fiber-reinforced composite plastic product include a method of using an intermediate material obtained by impregnating a matrix resin in reinforcements such as long fiber reinforcements, that is, prepreg. According to this method, it is easy to manage the content of the reinforcement fiber in the fiber-reinforced composite plastic product and it is possible to set the content to be high.
Examples of a detailed method of obtaining the fiber-reinforced composite plastic product from prepreg include a method of using an autoclave, a press molding, and the like. In order to cure the prepreg by these methods, a heating treatment of about 1 hour is required. If the time of the rising and falling of temperature is also included, under a general processing condition, a long period of time such as about 2 to 6 hours is required for one molding and thus molding costs are increased. Meanwhile, for the mass production of a product, molding needs to be performed at a relatively low temperature of about 100 to 150° C. over a short period of time such as several minutes to several tens of minutes.
One of the methods of performing molding in a short period of time is using an epoxy resin composition which has high reaction activity and a curing reaction which starts at a low thermal energy as a matrix resin. This method can shorten the curing time for the epoxy resin composition.
However, if reaction activity is excessively high, the curing reaction progresses even during storage at room temperature and storage stability deteriorates. In addition, since cross-linking density is increased, the obtained cured material is fragile and, in particular, is inferior to impact resistance.
With such background circumstances, there is a need for an epoxy resin composition, which can be completely cured in a short period of time even at low temperatures and uses as prepreg matrix resin, able to manufacture a fiber-reinforced composite plastic product with excellent mechanical properties and, more particularly, excellent impact resistance (toughness).
As prepreg which can be molded at relatively low temperatures in a short period of time, Patent Document 1 discloses prepreg which uses an epoxy resin composition, with polyvinyl formal as a thermoplastic resin elastomer, as a matrix resin, and uses dicyandiamide as a latent hardener. In addition, Patent Document 2 discloses prepreg consists of epoxy resin composition including a reactive product of an epoxy resin and an amine compound including a sulfur atom in its molecule.
In addition, as a method of improving impact resistance of a cured material, many methods are reported which use an epoxy resin composition including a thermoplastic resin. For example, Patent Documents 3 and 4 suggest the use of an epoxy resin composition containing a polyamide-based thermoplastic elastomer.
[Patent Document 1] Japanese Patent Publication No. 3796953
[Patent Document 2] International Publication No. 2004/048435
[Patent Document 3] Japanese Unexamined Patent Publication No. 8-337707
[Patent Document 4] Japanese Patent Publication No. 3539603